Borderline personality disorder (BPD) is frequently seen in clinical practice. Over the past 2 decades, research on BPD has increased substantially, with concomitant specialized psychotherapies that have been proved to be effective. A number of pharmacological agents have also been investigated, but results have been mixed.1

One of the enduring challenges in treating patients with BPD is that only a minority have straightforward clinical presentations with no comorbidity. BPD typically coexists with depression, anxiety, and substance abuse. Symptoms of these conditions may lead the clinician to miss the diagnosis of personality disorder entirely.

Comorbidities in BPD reflect a connection with both internalizing and externalizing disorders and symptoms. This indicates that unlike many other disorders that are more strongly associated with either internalizing or externalizing symptoms, BPD is associated with domains of symptoms and categories of disorders. Studies have found a mean of 4.1 lifetime Axis I comorbidities and 1.9 lifetime Axis II comorbidities for patients with BPD.2

TABLE 1 Lifetime comorbidities in patients with BPD

Diagnosis

Mood disorders prevail with Axis I comorbidities: 96% of patients with BPD have a mood disorder during their life, and lifetime depression is reported at 71% to 83%.2,3 Anxiety disorders are also extremely common: 88% of patients have an anxiety disorder, 34% to 48% have panic disorder, and 47% to 56% have PTSD. Alcohol and substance abuse or dependence are reported by 50% to 65%; eating disorders affect 7% to 26% over a lifetime (Table).2,3 Gender differences in these disorders are similar to what is seen in the general population: substance use disorders are more common comorbidities in males, and mood disorders and eating disorders are more common comorbidities in females.

Structured interviews, such as the Diagnostic Interview for Borderlines–Revised and the Structured Clinical Interview for DSM-IV, can confirm diagnoses of BPD and comorbid disorders.4,5 However self-report questionnaires designed for screening may inaccurately label patients who have BPD with another disorder. For example, the Mood Disorder Questionnaire often inaccurately identifies bipolar disorder in patients with BPD.6 Proposed changes in DSM-5 would not have solved this problem, since traits of negative affectivity, including anxiousness and depressivity, are associated with many other diagnoses. In the end, most of these comorbidities could be considered artifactual and BPD should often be considered as a primary diagnosis. The broader problem is that in DSM diagnoses, clear delineations between disorders or between traits and disorders are lacking.

Treatment

Patients with BPD need treatment specific to the disorder, whatever comorbidities they have. There are now many specialized forms of psychotherapy for BPD backed up by clinical trials, particularly dialectical behavior therapy, mentalization-based treatment, and Systems Training for Emotional Predictability and Problem Solving, among others.

Many treatments for other psychiatric disorders, both psychotherapeutic and psychopharmacological, are less likely to be effective in BPD, and antidepressants in particular yield disappointing effects in treating MDD. In addition, if psychopharmacological treatment is provided and more than one clinician is involved, good communication between team members is essential. This applies to situations in which a prescribing physician and a therapist are treating the same patient and to situations in which there are multiple prescribing physicians, such as a mood disorders specialist and a substance use disorder specialist. Clear communication helps avoid splitting that can easily occur, especially when different treatment approaches are used at the same time.

Finally, be wary of providing too much treatment. There is no evidence in this population that more is better, and one of the guiding principles of treatment is to have patients build a life worth living. If life consists of frequent appointments with therapists and groups for several years, this may prevent patients from having activities outside of treatment and impede generalization of what they are learning in psychotherapy.

What new information does this article provide?

? This article summarizes the management of comorbidities in patients with borderline personality disorder (BPD). Despite advances in the treatment of BPD, management of comorbidities has been neglected: this article summarizes the literature and presents a framework for management of these difficult cases.

What are the implications for psychiatric practice?

? Patients with BPD are frequently encountered in clinical practice and most have multiple comorbidities. This article will help clinicians guide these patients to the most beneficial treatment options while avoiding unnecessary and ineffective treatments.

Specific comorbidities in BPD

MDD is the most ubiquitous comorbidity in BPD. However, even patients who meet criteria for MDD may not benefit from antidepressants. The reasons for this are unclear, but some of the symptoms of MDD overlap with symptoms and associated features of BPD. For example, chronic dysphoria as seen in BPD is similar to sadness and worthlessness as experienced in MDD. Therefore, using treatments for MDD to target chronic dysphoria is less likely to be effective without additional treatment specific to BPD. In a study of 161 patients, of whom 42% had a current major depressive episode, improvement in BPD symptoms led to later improvement in major depressive symptoms, but the inverse was not true.7 This suggests that specific treatment for BPD may be an effective treatment for both disorders.